In Schroeder U.S. Pat. No. 4,148,372 the correct value of a resistor pellet, to be installed in the ignition key, was determined, during the last stages of vehicle assembly, by measuring the value of resistance in a bridge circuit contained in the electronic anti-theft controller located remotely from the ignition lock. In other words, it was necessary to match the correct key with the previously installed anti theft controller. Further, since the resistor is engaged by mechanical contacts located in the ignition lock assembly, it is possible for the rightful owner to be locked out of the vehicle due to intermittent opening of the contacts during operation of the ignition lock assembly. In Kaplit U.S. Pat. No. 4,144,523 a digital key assembly is provided which includes a programmable read only memory which is automatically programmed with the code for unlocking the system during initial removal of the key from the lock. However, the memory cannot be subsequently reprogrammed.